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List:       mythtv-users
Subject:    Re: [mythtv-users] Question on 8GB of RAM. Was: 32 bit or 64bit???
From:       Francis Hartojo <fhartojo () gmail ! com>
Date:       2009-01-17 5:47:53
Message-ID: ce5a82240901162147g6ddc9deaobf1f3909bed19e6c () mail ! gmail ! com
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On Fri, Jan 16, 2009 at 2:48 PM, Larry Finger <Larry.Finger@lwfinger.net> wrote:
> John Drescher wrote:
>
>> I forgot to say no problems at work with the 8GB M2N-E boards...
>>
>
> One of the places that systems can fail with the increase from 4 to 8
> GB ram is due to devices with 32-bit interrupt vectors and a driver
> bug in setting up and handling DMA memory. It is certainly possible
> that the devs for your devices did not have 8 GB. The most I've ever
> had is 4.
>
> You can partially test the drivers by adding a "mem=4G" line to your
> boot options. If the MB has a problem with a full population of
> memory, that may still show up, but the DMA problem will not.

What he said.  In my case, the problem isn't so much the >4GB RAM, but
the CPU itself and how it works in 64-bit.  Apparently, I'm running
into a rather well-known TLB bug with Phenom 9x00 Quad Core BE chips.
The motherboard (i.e., an Asus M3A) has a workaround switch in the
BIOS, so I switched that on.  Seems to help, but Live TV still
eventually freezes although not nearly as often and as easily.
Alternatively and quite strangely I can also make it more stable if I
limit the # of cores to 2 via the kernel "maxcpus=2" command-line
parameter.  I don't understand why this appears to be so.  There's an
article on Tom's Hardware about the third core in some AMD Quad Core
chips being bad, but I don't understand it's got to with TLBs.  One of
these days I'll post a more detailed summary of the problem on the
Ubuntu forum in case someone else runs into it.

FWIW.
-- 
Francis
echo "sunegbwb@tznvy.pbz" | tr '[a-z]' '[n-za-m]'
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